For one flicker of a second, her mask cracked. “You don’t know what it’s like to hear silence and feel safe .”

“It’s quiet,” Phineas whispered. “Too quiet.”

Phineas looked at Ferb. Ferb nodded once.

Phineas laughed. “Let’s not tell her.”

One rainy Tuesday, while Ferb was quietly tuning a theremin-powered ceiling fan, the backyard shed shuddered. A disc of blue energy sliced the air. From it tumbled a battered, half-melted platy-pus-shaped helmet.